1. Field of the Invention
The present invention relates to a semiconductor optical device.
2. Related Background Art
The semiconductor optical device includes an n-type semiconductor substrate, a semiconductor optical waveguide disposed on a surface of the semiconductor substrate, a burying portion disposed around the semiconductor optical waveguide, and a p-type clad layer disposed on the semiconductor optical waveguide and the burying portion. The burying portion buries the semiconductor optical waveguide. The semiconductor optical waveguide includes an n-type semiconductor layer disposed on the n-type semiconductor substrate, an active layer disposed on the n-type semiconductor layer, and a p-type semiconductor layer disposed on the active layer. The burying portion is constituted of two semiconductor films, and includes a p-type semiconductor film disposed on the n-type semiconductor substrate, and an n-type semiconductor film disposed on the p-type semiconductor film. The semiconductor optical device includes a cathode electrode disposed on the backside of the n-type semiconductor substrate, and an anode electrode disposed on the p-type clad layer.
In the semiconductor optical device, the n-type substrate and the p-type semiconductor film of the semiconductor burying portion forms a pn junction, the p-type clad layer and the n-type semiconductor film of the buried portion forms a pn junction, and the p-type semiconductor film and the n-type semiconductor film of the semiconductor burying portion forms a pn junction. When an electrical signal is applied between the anode electrode and the cathode electrode of the semiconductor optical device, a reverse bias voltage is applied to one of the pn-junctions. The reverse-biased pn junction of the burying portion blocks electric current and no electric current flows through the burying portion including the reverse-biased pn-junction. But the reverse-biased pn junction produces depletion capacitance. According to the inventors"" studies, the capacitance in the burying portion should be reduced in order to enable the semiconductor optical device to operate at a high speed.
It is an object of the present invention to provide a semiconductor optical device having a structure capable of reducing the capacitance.
One aspect of the present invention is a semiconductor optical device. The semiconductor optical device comprises: a semiconductor substrate; a semiconductor portion; a multilayer semiconductor portion; and a second conductive type semiconductor layer. The semiconductor substrate has a first conductive type thereof. The semiconductor portion includes first and second III-V compound semiconductor layers and an active layer. The semiconductor portion is provided on the semiconductor substrate, and the semiconductor portion has a side face extending in a direction of a predetermined axis. The active layer is provided between the first and second III-V compound semiconductor layers. The multilayer semiconductor portion is provided on the semiconductor substrate and the side face of the semiconductor portion. The second conductive type semiconductor layer is provided on the semiconductor portion and the multilayer semiconductor portion. The multilayer semiconductor portion has first to fourth semiconductor layers sequentially arranged on the semiconductor substrate. The first semiconductor layer is a second conductive type III-V compound semiconductor layer extending on the side face of the semiconductor portion and the semiconductor substrate. The second semiconductor layer is a first conductive type III-V compound semiconductor layer provided on the first semiconductor layer. The third semiconductor layer is a second conductive type III-V compound semiconductor layer extending on the second semiconductor layer. The fourth semiconductor layer is a first conductive type III-V compound semiconductor layer provided on the third semiconductor layer. Each semiconductor layer of the first to fourth semiconductor layers and a semiconductor region adjacent to the semiconductor layer constitutes one of a pn junction and a pin junction.
The semiconductor optical device according to the present invention further comprises: a first electrode and a second electrode. The first electrode is electrically connected to the first III-V compound semiconductor layer of the semiconductor portion. The second electrode is electrically connected to the second III-V compound semiconductor layer of the semiconductor portion.
According to another aspect of the present invention, a semiconductor optical device comprises: a first conductive type III-V compound semiconductor portion; a second conductive type III-V compound semiconductor portion; a semiconductor portion; and a multilayer semiconductor portion. The first conductive type III-V compound semiconductor portion extends along a first reference plane intersecting a predetermined axis. The second conductive type III-V compound semiconductor portion extends along a second reference plane intersecting the predetermined axis. The semiconductor portion has side faces. The semiconductor portion is provided between the first conductive type III-V compound semiconductor portion and the second conductive type III-V compound semiconductor portion. The semiconductor portion includes first and second III-V compound semiconductor layers and an active layer. The active layer is provided between the first and second III-V group compound semiconductor layers. The multilayer semiconductor portion has first to fourth semiconductor layers. The first to fourth semiconductor layers are provided between the first conductive type semiconductor portion and the second conductive type semiconductor portion. The multilayer semiconductor portion is provided on the side faces of the semiconductor portion. Each layer of the first to fourth semiconductor layers is adjacent to semiconductor regions of the following: the remaining of the semiconductor layers of the first to fourth semiconductor layers; the first conductive type III-V compound semiconductor potion; and the second conductive type III-V compound semiconductor portion. Each of the first to fourth semiconductor layers has a conductive type different from that of the adjacent semiconductor region.
The semiconductor optical device according to the present invention further comprises: a first electrode; and a second electrode. The first electrode is electrically connected to the first III-V compound semiconductor layer of the semiconductor portion. The second electrode is electrically connected to the second III-V compound semiconductor layer of the semiconductor portion.
In the semiconductor optical device, the first semiconductor layer of the multiplayer semiconductor portion includes first and second layered semiconductor regions. An impurity concentration of the first layered semiconductor region is lower than that of the second layered semiconductor region. The first layered semiconductor region is provided between the second layered semiconductor region and the substrate. The impurity concentration of the first layered semiconductor region is lower than that of the substrate.
The semiconductor optical device according to the present invention further comprises a pair of trenches provided in the first to fourth semiconductor layers of the multilayer semiconductor portion. The semiconductor portion is located between the trenches.
In the semiconductor optical device, the active layer includes a light generating region provided for a semiconductor light generation element.
In the semiconductor optical device, the active layer includes an optical absorption region provided for an optical modulator.
In the semiconductor optical device, the active layer includes an optical absorption region provided for a semiconductor photodetector.
In the semiconductor optical device, the semiconductor portion includes a first portion provided to constitute one of an optical modulator and a semiconductor photodetector, and a second portion provided to constitute a semiconductor light generation element. An impurity concentration of the first semiconductor layer has a highest value smaller than that of the second semiconductor layer.
In the semiconductor optical device, the semiconductor portion includes a first portion provided to constitute one of an optical modulator and a semiconductor photodetector, and a second portion provided to constitute a semiconductor light generation element. An impurity concentration of the first semiconductor layer has a highest value smaller than that of the semiconductor substrate. An impurity concentration of the second semiconductor layer is larger than the highest value of the impurity concentration of the first semiconductor layer.
In the semiconductor optical device, the semiconductor portion includes a first portion provided to constitute one of an optical modulator and a semiconductor photodetector, and a second portion provided to constitute a semiconductor light generation element. The first semiconductor layer of the multilayer semiconductor portion includes first and second layered semiconductor regions. An impurity concentration of the first layered semiconductor region is lower than that of the second layered semiconductor region. The first layered semiconductor region is provided between the semiconductor substrate and the second layered semiconductor region.
According to still another aspect of the present invention, a semiconductor optical device comprises: a semiconductor substrate; a semiconductor portion; a multilayer semiconductor portion; and a second conductive type semiconductor layer. The semiconductor substrate has a first conductive type. The semiconductor portion includes first and second III-V compound semiconductor layers and an active layer. The semiconductor portion is provided on the semiconductor substrate. The semiconductor portion has a side face extending in a direction of a predetermined axis. The active layer is provided between the first and second III-V compound semiconductor layers. The multilayer semiconductor portion is provided on the semiconductor substrate and the side face of the semiconductor portion. The second conductive type semiconductor layer is provided on the semiconductor portion and the multilayer semiconductor portion. The multilayer semiconductor portion has first to 2n-th semiconductor layers sequentially arranged on the semiconductor substrate, where the number n is equal to or more than two. The first semiconductor layer is provided on the semiconductor substrate and the side face of the semiconductor portion. The 2m-th semiconductor layer is a first conductive type III-V compound semiconductor layer, where the number m is integer and not more than n. The (2mxe2x88x921)-th semiconductor layer is a second conductive type III-V compound semiconductor layer. Each layer of the first to 2n-th semiconductor layers is adjacent to another layer of the first to 2n-th semiconductor layers to constitute one of a pn junction and a pin junction.
According to still another aspect of the present invention, a semiconductor optical device comprises: a first conductive type III-V compound semiconductor portion; a second conductive type III-V compound semiconductor portion; a semiconductor portion; and a multilayer semiconductor portion. The first conductive type III-V compound semiconductor portion extends along a first reference plane intersecting a predetermined axis. The second conductive type III-V compound semiconductor portion extends along a second reference plane intersecting the predetermined axis. The semiconductor portion has side faces. The semiconductor portion is provided between the first conductive type III-V compound semiconductor portion and the second conductive type III-V compound semiconductor portion. The semiconductor portion includes first and second III-V compound semiconductor layers and an active layer. The active layer is provided between the first and second III-V group compound semiconductor layers. The multilayer semiconductor portion has first to 2n-th semiconductor layers. The first to 2n-th semiconductor layers is provided sequentially between the first conductive type semiconductor portion and the second conductive type semiconductor portion. The multilayer semiconductor portion is provided on the side faces of the semiconductor portion. The 2m-th semiconductor layer has a first conductive type, where the number m is integer and not more than n. The (2mxe2x88x921)-th semiconductor layer has a second conductive type. Each layer of the first to 2n-th semiconductor layers is adjacent to another layer of the first to 2n-th semiconductor layers to constitute one of a pn junction and a pin junction.
The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.